Potential biochemical markers of uterine receptivity.

Implantation in humans is a complex process that involves embryo apposition and attachment to the maternal endometrial epithelium, traversing adjacent cells of the epithelial lining, and invasion into the endometrial stroma. These processes involve a variety of molecules which are not unique in themselves, but play unique roles in the process of implantation. The molecular dialogue that occurs between the implanting conceptus and the endometrium involves cell-cell and cell-extracellular matrix interactions, mediated by lectins, integrins, matrix degrading enzymes and their inhibitors, prostaglandins, and a variety of growth factors, cytokines, and angiogenic peptides, their receptors and modulatory proteins. It is likely that each of these, when appropriately expressed or inhibited, contributes to endometrial receptivity or non-receptivity to an implanting conceptus. Currently, a working definition of a receptive versus a non-receptive endometrium is incomplete. While histological normality of the endometrium does not necessarily imply functional normality, temporal and spatial expression of particular biochemical principles in the endometrium are highly suggestive of functional roles of these principles in implantation and endometrial receptivity. These potential markers of endometrial receptivity are discussed herein. It is envisioned that as regulation of these markers is elucidated, their expression may be manipulated to improve implantation rates and fertility or to limit implantation for successful contraception.